Heterogeneous deployment has been considered by, the Third Generation Partnership Project (3GPP) Long-Term Evolution-Advanced (LTE-A) working groups as a technique to substantially improve system capacity and coverage. In a heterogeneous deployment, low power network nodes such as pico evolved Node-Bs (eNBs) and femto eNBs are overlaid with traditional high power eNBs which can be referred to as a macro eNBs. Such macro, pico, and femto eNBs form macro, pico, and femto cells, respectively. The term “cell” refers to an area of coverage of wireless transmission by a network, such as an eNB. In some instances, each of pico cells or femto cells can have a coverage at least partially overlapping with the coverage of the macro cell. To efficiently utilize the radio spectrum, in one embodiment macro, pico and femto cells are deployed on the same carrier. However, full frequency reuse among pico, femto and macro cells could introduce severe inter-cell interference.
In particular, to improve the system capacity, range expansion has been introduced for pico eNBs where a user equipment (UE) could connect to the pico eNB even when the signal from the macro eNB is stronger. Similarly, in closed subscriber group (CSG) femto cells, the UE may receive a stronger signal from the femto cell than from the macro eNB. However, if the UE is not part of the closed subscriber group, the UE may need to connect to the macro eNB. The weaker cell that the UE is connecting to is referred to herein as the victim cell. In such an instance, the stronger cell that the UE is not connecting to can be referred to as the aggressor cell in the context of this document.
One solution to reduce interference in a victim cell is almost blank sub-frame (ABS) based enhanced inter-cell interference coordination (eICIC). In this solution, the higher powered cell blanks out transmission or lowers transmitting power on certain sub-frames to allow signaling from the lower powered (victim) cell. However, the almost blank sub-frame still contains cell-specific reference signals (CRS), which are sent during the ABS, causing degraded reception for various control and data channels, including the Physical Control Format Indicator Channel (PCFICH), the Physical Hybrid Automatic Repeat Request (HARQ) Indicator Channel (PHICH) the Physical Downlink Control Channel (PDCCH) and the Physical Downlink Shared Channel (PDSCH). However, the PHICH, PDCCH and PDSCH can utilize multiple orthogonal frequency divisional multiplexing (OFDM) symbols and can thus be transmitted beyond the CRS-polluted OFDM symbols. Conversely, the PCFICH cannot be reliably detected under the CRS interference since the PCFICH is transmitted in the first OFDM symbol only and thus experiences significant interference from CRS.